Method of cracking petroleum hydrocarbons



Feb, 16, 1932. w, M, CROSS 1,845,959

METHOD OF CRACKING PETROLEUM HYDROCARBONS Filed June 22, 1928 BUBBLETOWER COOLER REA CT/ 0N CHA MBER F l/RNACE I N VEN T0 R Patented Feb.18, 1932 lTD STATES PATENT OFFICE WAL'JEEJB. M. CROSS, OF KANSAS CITY,MISSOURI, ASSIGNOR IO GASOLINE PRODUCTS UOIVDE'ANY, INCL, OF WILMINGTON,DELAWARE, A CORPORATION OF; DELAWARE Ilv'IETHOID F CRACKING PETROLEUMHYDROCARBONS Application filed June 22,

This invention relates to improvements in a method of cracking anddecomposing petroleum hydrocarbons to produce lighter from heavierboiling point products and to manufacture a motor fuel adapted forinternal combustion engines.

The novelty of the invention lies primarily in the combination of steamwith the hydrocarbon products after they have been raised y to arelatively high temperature and subsequent superheating of thehydrocarbons in the presence of steam to effect additional decompositionand rearrangement ofthe molecules and what is hereinafter termed asselective oxidation of the hydrocarbons in which the mixture of oil andsteam is carried to a sufficiently high temperature to form earbonmonoxide and hydrogen which appears to re-combine with the gumminghydrocarbons and carbonaceous material separated during the incipientdecomposition of the oil, thus retarding the decomposition andaccumulation of the separated polymers in tubes.

The single figure is a diagrammatic side elevational view of a type ofapparatus in which the process may be carried on, with parts in sectionand parts broken away.

Referring to the drawings, at 1 is shown a furnace in which ispositioned a heating coil an separated into two sections designated as 2and 3. Adjacent the furnace 1 is a second furnace or superheater 4 inwhich is positioned a superhcating coil 5. The discharge end of thesuperheating coil communicates 35 with the reaction chamber 6 whichispref erably fabricated of a single ingot of forged steel. Thischamberhas removable ends to facilitate cleaning and is heavilyinsulated to prevent heat by radiation.

At 7 is shown an evaporator connected by a transfer line 8 to thereaction chamber 6 and in this line 8 is interposed a reduction valve 9.The top of the evaporator 7 is connected by a vapor line 10 to adephlegmating is or refluxing tower 11, preferably of a bubble 1928.Serial N0. 237,400.

type. The bottom of the evaporator is equipped with a draw-off line 11controlled by a valve 12 automatically manipulated by a liquid levelregulating device 13. The line 11 terminates in a cooling coil 14.

The dephlegmating tower has a bottom draw-off line 15 controlled by avalve 16 automatically regulated by the liquid level regulating device17. A vapor line 18 is conneete'd to the top of the tower and terminatesin a condensing coil 19 positioned in the condenser box 20. Thedischarge end of the coil 19 connects with a pipe 21 which communicateswith a gas separator 22. This gas separator is likewise equipped with agas relief line 23 controlled by a valve 24: and a bottom liquidwithdraw line 25 regulated by a valve 26 manipulated automatically by a.liquid level regulating device 27.

In operation, oil is introduced from any convenient source through thepipe 28 and is passed through a pre-heating coil 29 positioned in thetopof the dephlegmating tower. From the coil 29 the preheated oil isdirected through the line 30, is picked up by the pump 31 and charged tothe upper heating coil section 2 in the furnace 1. From the upper bankof tubes the oil passes through the transfer line 32 into the lower bankof tubes 3 where additional heat is added.

At a point intermediate of the inlet and discharge of the passage of theoil through the furnace, preferably at a position designated by the pipe33, steam is introduced and combined with the hydrocarbons passing.

the tubes 5, and this thermo-couple regulates the valve which controlsthe fuel supplied to the burner 34. Combustion gases, after being passedover the tubes 5, are discharged through a breeching 37 into the mainfurnace 1 to supplement heat applied to the tube banks 2 and 3.

After being superheated in the tubes 5, the oil is discharged into thereaction chamber where it collects in a considerable body, and in thisstage the cracking which is initiated in the tubes 2, 3 and 5, issubstantially consummated. The pressure maintained upon the heatingtubes and reaction chamber and the apparatus up to the valve 9 rangesfrom 500 to 1000 pounds per square inch. Normally pressures of the orderof from 600 to 700 pounds are utilized, although higher pressures aremore feasible with certain types of oil.

The cracked hydrocarbon products are discharged from the opposite end ofthe reaction chamber 6 through the transfer line 8, pressure beingreduced at the valve 9. The pressure maintained in the apparatussubsequent to the chamber 6 is normally only sufficient to overcomefriction in the apparatus, but where'operation and quality of theultimate distillate is to be improved, super-atmospher ic pressures of200 to 250 pounds may be maintained upon the evaporating anddephlegmating stages.

In the evaporator the heavier and lighter hydrocarbons are separated bydistillation, the lighter materials passing overhead through the line10110 the refluxing tower 11.

The heavier materials accumulate in the bottom of the evaporator, andare drawn off through the pipe 11' and directed to a cooler 14:, afterwhich they are diverted to storage or to subsequent further methods oftreatment, such as in coking stills, for the separation of the freecarbon and distillable fractions.

The vapors passing into the refluxing tower through the pipe 10 rise andare contacted by a wash oil flowingin a counter-current direction totherising vapors. The temperatures in the towers are-so controlled that thevapor passing overhead through the line 18 constitutes substantially thefractions com prising the ultimate distillate. This overhead material isdrawn off through the line 18 and condensed in the condensing coil 19after which it is collected in the gas separator 22. The gas is takenoff from the separator through the line 23 and the distillate throughthe bottom liquid withdrawal line 25. V

Refluxing condensate accumulating in the tower 11 is withdrawn throughthe pipe 15, is picked up by the pump 38 and re-circulated through theline 39 to the suction side of the pump 31 by means of which it is againintroduced into the system.

It has been found in actual practice in cracking hydrocarbons attemperatures in excess of 700 at pressures in excess of 500 pounds, thatcarbon has a tendency to collect in the transfer line between theheating tubes and the reaction chamber or in the tubes near thedischarge end of the heating bank. This accumulation may necessitateshutting down the operation for cleaning at intervals, and toward theclose of the run retards considerably the normal operation of theapparatus. It has been found that if steam is introduced to the heatingtubes and superheated with the hydrocarbons to temperatures of the orderof 1000 F. in the coil bank 5, the steam will combine with the resinousmaterial and free carbon which is separated during the cracking of theoil to form substantially carbon monoxide and hydrogen, thus preventingthe accumulation of the polymers and carbonaceous material on the tubes,and eliminating difliculties or clogging of the tubes from this source.To effect this type of operation it is advisable to maintain thetemperatures in the supplementary heater 4 relatively constant, and forthis purpose a thermo-couple 40 is attached to the surface of one ormore of the tubes and set at a predetermined temperature. When the tubesurface reaches this temperature the thermo-couple causes the diaphragmor electrical manipulating device 41 to which it is connected, tothrottle the fuel control valve of the burner 34, thus automaticallycontrolling the combustion temperature of the gases in the furnace 4:.

By maintaining these tubes at a metal temperature of around 1000 and anoil temperature of the order of 900 F., it has been found that the steamintroduced through the line 33 decomposes and combines with the polymersseparated out during the cracking operation.

It has also been found in actual operation that under these conditions agasoline is produced having improved anti-detonating qualities. Amid-continent gas oil operated on in this manner had anti-detonatingqualities equal to a gasoline produced from ordinary parafiin base crudegasoline when blended with 40% of benzol, so that the cracked distillateremoved from a process of this character when operating on mid-continentgas oil, has substantially the characteristics of a .0% benzol blendgasoline distillate.

The particular reaction that takes place 12 is unknown, though it isthought that there is a selective oxidation created by the presence ofthe steam, or that the steam has a hydrogenating effect upon thepolymerized material.

The process contemplates any type of operation in which steam iscombined with hydrocarbons during heating, and the mixture superheatedtothe extent that the constitucombined with the hydrocarbon constituentsto prevent the accumulation of polymers and carbonaceous material in theheating tubes.

llt is obvious also that the elimination of deposition in the heatingcoils and superheating coils 5 diminishes the amount of separatedpolymerized material accumulating in the reaction stage.

A typical operation on mid'continent gas oil having a gravity of 32 to33 Baum,

would be to heat the oil to a temperature of 700 to 800 F. in theheating coil and raise the temperature in the superheating coil 5 to 900to 950 F, while temperatures in the reaction chamber would recede tofrom 700 to 800 l5. T he pressure, as suggested, would be in the orderof 500 to 1000 pounds per square inch in the heating and reaction stagesup to the reduction valve 9.

"l he oil is heated in separate zones which may be identified as a.primary heating stage and a secondary heating stage which correspond tothe initial stage of heating and a stage of superheating. In the primaryheating stage the oil is raised to a temperature of incipient crackingor to a degree of heat where the separation of polymerized mate.- rialis not excessively formed or formed to the extent that considerabledeposition occurs in the tubes. In the secondary or superheating zonesutiicient heat is supplied so that the heat is added at a greater ratethan it can be carried away by the oil passing through the tubes, andthis excessive heating of the tubes or metal surrounding the circulatingoil is automatically controlled so that the walls of the tubes carryingthe oil shall be heated to a temperature substantially higher than thetemperature of the oil, and in the neighborhood of 1000 F. or above.This excessive temperature to which the metal in the tubes in thesuperheating stage is raised may be defined broadly as that termperature at which the carbonaceous or gumming hydrocarbons separatedduring the heating will be oxidized by the constituents of the steampresent with the oil to produce carbon monoxide and hydrogen.

ll claim as my invention:

1. A. process of cracking hydrocarbon oils to increase theanti-detonating properties thereof comprising the steps of heating theoil to a conversion temperature in a heating zone, subsequentlysupplying steam to the hydrocarbons at an intermediate stage in theheating zone, raising the temperature of the hydrocarbons after theintroduction of steam sutliciently high to produce a selective oxidationof the polymers separated during heating, collecting the hydrocarbons inan enlarged body in liquid phase, and maintaining superatmosphericpressure thereon, passing the products of conversion from the enlargedbody to an evaporating zone maintained at a pressure lower than that atwhich the conversion is carried out whereby a portion of the products ofconversion will be vaporized, and then separating the lighter from theheavier vaporous fractions by fractionation.

2. A process of cracking hydrocarbon oils to increase theanti-detonating properties thereof comprising the steps of heating theoil to a conversion temperature in a heating zone, subsequentlysupplying steam to the hydrocarbons at an intermediate stage in theheating zone, raising the temperature of the hydrocarbons after theintroduction of steam sufliciently high to produce a selective oxidationof the polymers separated during heating, collecting the hydrocarbons inan enlarged body in liquid phase and maintaining superatmosphericpressure thereon, passing the products of conversion from the enlargedbody to an evaporating zone maintained at a pressure lower than that atwhich the conversion is carried out whereby a portion of the products ofconversion will be vaporized, then separating the lighter from theheavier vaporous f actions by fractionation, and recycling the refluxcondensate to the heating zone.

3. A process of cracking hydrocarbon oils to increase theanti-detonating properties thereof and retard carbon accumulationscomprising the steps of heating the oil to a conversion temperatureunder high pressure, combining steam with the highly heated oil, furtherheating the oil at high temperatures and effecting a combination of theconstituents of the steam and polymers separated from the oil duringheating by superheating the mixture of oil and steam, affording time forcompleting the reaction by collecting the highly heated products ofconversion in an enlarged body in a reaction zone without anysubstantial reduction in temperature and pressure, passing the productsof conversion from the reaction zoneto a vaporizing zone maintained atreduced pressures whereby the lighter fractions will be vaporized, andsub jecting the vaporized fractions to fractionation to separate thelighter from the heavier fractions.

4;. A process of cracking hydrocarbon oils to increase theanti-detonating properties thereof and retard carbon accumulationscomprising the steps of heating the oil to a conversion temperatureunder high pressure, combining steam with the highly heated 011, furtherheating the oil at high temperatures and effecting a combination of theconstituents of the steam and polymers separated from the oil duringheating by superheating the mixture of oil and steam, affording time forcompleting the reaction by collecting the highly heated products ofconversion in an enlarged body in a reaction zone without anysubstantial reduction in temperature and pressure, passing the productsof conversion from the reactlon zone to a vaporizing zone 4- p, r I1,845,959

maintained at reduced. pressures whereby the lighter fractions will bevaporized; subjecting the vaporized fractions to fractionation toseparate the lighter from the heavier fractions, preheating the oil tobe treated by passing the same in; heat exchange relation with thevapors to be fractionated, mixing the preheated oil with refluxcondensate from the fractionation ofthe vapors, and introducing the sameinto the heating zone.

WALTER M. CROSS.

